1. Field of the Invention
The present invention pertains to telecommunications, and particularly to using Internet Protocol (IP) with and/or in a radio access network (RAN).
2. Related Art and Other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to the one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which is in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25 external networks)
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The circuit switched aspects of the Iu Interface are termed the “Iu-CS” Interface; the packet switched aspects of the Iu Interface are termed the “Iu-PS” Interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. In some instances, a connection involves both a Source RNC (SRNC) and a Drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC (see, in this regard, U.S. patent application Ser. No. 09/035,821 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Measurement Transfer”; and U.S. patent application Ser. No. 09/035,788 filed Mar. 6, 1998, entitled “Telecommunications Inter-Exchange Congestion Control”). The interface between a SRNC and a DRNC is termed the “Iur” interface.
A project known as the Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM-based radio access network technologies. A user plane protocol for 3GPP-99 is illustrated in FIG. 7. FIG. 7 particularly shows (as the left stack) the user plane protocol stack for the Iu-CS, Iur, and Iub Interfaces and (as the right stack) the user plane protocol stack for the Iu-PS Interface. As shown in FIG. 7, the user plane protocol stack is divided between a radio network layer and a transport network layer. Portions of the 3GPP-99 user plane protocol stack which are attributable to the transport network layer are shaded in FIG. 7. The transport network layer provides transport services needed by the radio network layer.
As apparent from FIG. 7, the lower protocols of stacks for the 3GPP-99 user plane protocol stacks employ Asynchronous Transfer Mode (ATM) technology. ATM is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and have a fixed size. An ATM cell consists of 53 octets, five of which form a header and forty eight of which constitute a “payload” or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual path is a principal path defined between two switching nodes of the network; the virtual channel is one specific connection on the respective principal path.
A protocol reference model has been developed for illustrating layering of ATM. The protocol reference model layers include (from lower to higher layers) a physical layer (including both a physical medium sublayer and a transmission convergence sublayer), an ATM layer, and an ATM adaptation layer (AAL), and higher layers. The basic purpose of the AAL layer is to isolate the higher layers from specific characteristics of the ATM layer by mapping the higher-layer protocol data units (PDU) into the information field of the ATM cell and vise versa. There are several differing AAL types or categories, including AAL0, AAL1, AAL2, AAL3/4, and AAL5. Yet another AAL type, known as AAL2 prime, is described in the following (all of which are incorporated herein by reference: U.S. patent application Ser. No. 09/188,102, filed Nov. 9, 1998; U.S. patent application Ser. No. 09/188,347, filed Nov. 9, 1998; and International Patent Application Number PCT/SE98/02250 (WO 99/33315, published Jul. 1, 1999).
AAL2 is a standard defined by ITU recommendation 1.363.2. An AAL2 packet comprises a three octet packet header, as well as a packet payload. The AAL2 packet header includes an eight bit channel identifier (CID), a six bit length indicator (LI), a five bit User-to-User indicator (UUI), and five bits of header error control (HEC). The AAL2 packet payload, which carries user data, can vary from one to forty-five octets
An object of the present invention, in one aspect, is utilization of Internet Protocol in lieu of the ATM protocol in the user plane protocol stacks for various interfaces (e.g., Iu-CS Interface, Iur Interface, and Iub Interface) of a radio access network such as UTRAN, and in another aspect is provision of a new transport network layer protocol usable on these interfaces as well as on the Iu-PS Interface.